1. Field of the Invention
The present invention relates to a curable resin composition and, more particularly, to a curable resin composition which is provided with excellent properties such as curing rate, surface hardness, transparency and so on, in a balanced manner and which is capable of lending itself favorably and extensively to materials for forming a back coating layer, for example, of ink ribbons, materials for forming protective layers for various cards, films, molded or formed products and so on, coating materials of various optical devices and instruments, binders of various optical devices and instruments, binders for magnetic materials, and so on.
2. Description of Related Art
Curable resins and curable resin compositions are cured readily, for example, upon exposure to heat rays or activation energy rays so that they are used in wide fields for various coating materials, materials for forming protective layers, curing filler compounds, and so on.
In particular, curable phosphazene compounds are recognized for their utility because they are good in mechanical properties such as surface hardness, resistance to heat, and so on. For example, Japanese Patent Publication (kokoku) No. 2,449/1984 and Japanese Patent Publication (kokai) No. 241,075/1988 disclose methods for preparing curable phosphazene compound and reaction-curing coating materials.
Furthermore, Japanese Patent Publication (kokai) No. 47,406/1986 discloses curable resin compositions comprising a polymerizable phosphazene compound and a mixture of the said phosphazene compound with a polymerizable monomer such as 2,2'-bis(acryloxydiphenyl)propane, 2,2'-bis[4-(3-methacryloxy)-2-hydroxypropoxyphenyl]propane.
The curable resin compositions, however, have a limited utility for dental restoring materials and dental filler compounds. They are provided with improved mechanical strength and adhesion, but there is still left room for improvements in properties such as a curing rate and a degree of transparency.
Generally speaking, conventional curable resins and curable resin compositions can be said to be still insufficient in properties such as a curing rate, surface hardness, transparency, cure shrinkage and so on and, furthermore, they are not said to have their properties harmonized in a balanced fashion.